Also USGS Monograph 29, p. 17-18, pl. 34. Black Rock diabase. Volcanic plugs parallel with Holyoke Range and 1 mile southeast of it, intrusive into Triassic and Jurassic sediments [Newark group]. One is quartz diabase; others are similar to bedded trap rock but are fresher and form domes. Age is Triassic-Jurassic. Present in Mount Holyoke region.
Named from outcrops at Black Rock, south of Mount Holyoke House, Mount Holyoke quadrangle, Hampshire Co., central MA.
Source: GNU records (USGS DDS-6; Reston GNULEX); supplemental information from US geologic names lexicon (USGS Bull. 896, p. 206).
Pg. 272. Black Rock diabase is not an isolated intrusive plug as first supposed, but is a part of the Hampden diabase flow, of Newark group, which is interbedded in Longmeadow sandstone.
Source: US geologic names lexicon (USGS Bull. 896, p. 206); GNU records (USGS DDS-6; Reston GNULEX).
Black Rock diabase breccia dike in Granby tuff consists of fragments of diabase, tuff, and sedimentary rocks in diabase matrix. Cuts basal sediments above Holyoke diabase sheet.
Source: GNU records (USGS DDS-6; Reston GNULEX).
For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.
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